This invention relates to cannulas, especially those used for positioning and manipulating intravascular catheters known as angiographic catheters.
Angiography is a well-known and very valuable procedure used to diagnose vascular and organ disease. It involves the introduction of a hollow tubular catheter into one of the major arteries or veins, such as the femoral or brachial arteries, and advancing and maneuvering it into smaller branching vessels which are to be studied. After the catheter is in position, a radio-opaque fluid is injected through the catheter into the vascular system to be studied and an x-ray picture is taken of the now x-ray opaque vascular structure.
Prior art techniques for introducing such catheters include what is known as the "cut down" method and various modifications of the "Seldinger" technique. The "cut down" technique involves surgically opening a vein or artery and introducing the angiographic catheter directly through the incision. This method inevitably involves the loss of blood through the incision as well as venous ligation and arterial repair. The use of this method renders it particularly difficult to employ the same vessel when multiple studies are indicated.
The American Journal of Cardiology, Vol. 30, Sept., 1972, at page 378, describes an alternative method of cardiac catheterization, a modification of the Seldinger technique, wherein a percutaneous sheath is introduced into the lumen of a blood vessel. A hollow needle is inserted through the skin and into the lumen; a guide wire is passed through the needle and advanced up the artery or vein into the organ to be studied; the needle is removed, leaving the guide wire in the vessel; a sheath and dilator unit are advanced over the wire into the vessel, and; the dilator is removed along with the guide wire. Now, any type of catheter desired of similar diameter, can be inserted through the sheath into the vessel. To avoid excessive bleeding, and to ensure against the possibility of an air embolism, this technique requires the physician to occlude the orifice of the sheath during catheter changes. The procedure suffers from the possibility of a blood clot migrating to the heart, lungs, or extremities. Blood loss through the annular space between the sheath and the catheter is difficult to avoid.
Both these methods are also characterized, especially if multiple studies are indicated, by venous thrombosis, subcutaneous hematomas, and other considerable discomfort to the patient. Obviously, neither of these methods is totally satisfactory.